/in/foo.cc: In function 'std::vector<int> cal_difference_set()':
/in/foo.cc:50:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<va.size();i++)
                 ~^~~~~~~~~~
/in/foo.cc:53:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0;j<vb.size();j++)
                     ~^~~~~~~~~~
/in/foo.cc: In function 'void print(std::vector<int>)':
/in/foo.cc:77:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<vc.size();i++)
                 ~^~~~~~~~~~
/in/foo.cc:79:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if(i!=vc.size()-1)
            ~^~~~~~~~~~~~~